The present invention relates to a drum motor comprising a driving means, a gear transmission, and a driven means, said gear transmission being constructed as a plurality of planet transmissions in the form of sun wheels and planet wheels arranged successively in the interior of an internally toothed rim, said driven means being in the form of a cylindrical drum which contains the driving means and the toothed rim, and which rotates about a longitudinal axis A.
Drum motors of this type are generally known, see e.g. U.S. Pat. No. 5,429,558 and Danish Utility Model No. 95 00427.
A considerable problem associated with the conventional drum motors is that the production of drum motors having different gear transmissions requires a large number of different components, viz. toothed rims of lengths corresponding to the number of gear transmissions which are mounted internally in the drum motor. Furthermore, it is a considerable problem that the teeth of the toothed rim in the known drum motors are subjected to wear in the area at the last planet transmission most remote from the electric motor where a considerable force is to be transferred between the teeth. This wear has necessitated exchange of the entire toothed rim and thus resulted in increased operating costs.
The invention is intended to solve these problems, in that the toothed rim according to the invention is formed by at least two juxtaposed ring-shaped segments, and that means are provided to secure the ring-shaped segments against relative rotation about the longitudinal axis A.
In this context the term xe2x80x9cjuxtaposedxe2x80x9d means that the segments are arranged side by side to form a tubular body. The term xe2x80x9cring-shaped segmentsxe2x80x9d means relatively flat elements having teeth arranged on an internal wall which defines a circular through opening. The segments are moreover defined by a preferably approximately circular external wall opposite the teeth. The external wall, however, may assume another geometrical shape.
According to a preferred embodiment, the number of ring-shaped segments corresponds to the number of planet transmissions. Furthermore, the toothed rim may advantageously incorporate ring-shaped segments which are made of different materials, and which may thereby be adapted to the applied forces.
It is preferred that the securing means are formed by complementary engagement means provided on the ring-shaped segments, and that the ring-shaped segments have an identical geometrical shape. The latter gives considerable advantages in terms of economy and production. It is particularly preferred that the complementary engagement means are provided as recesses and projections formed on the external wall of the segments opposite the teeth.
In particular applications it may moreover be an advantage that the ring-shaped segments are embedded in a cylindrical jacket which secures the segments against relative rotation. The segments may hereby be constructed as simple, internally toothed rings or rims, which are secured by the embedment.
To facilitate mounting and to ensure a reliable guide of the planet transmissions, the ring-shaped segments may moreover be provided with stops which prevent displacement of the planet transmissions in a direction toward the longitudinal axis A.
The possibility of constructing the toothed rim segments with different internal diameters, but preferably substantially the same external diameter, provides a high degree of freedom in the selection of the transmission ratio of the drum motor.
The invention will be described more fully below with reference to two embodiments. In the drawing: